1. Field of the Invention
The present invention relates to a device for controlling rotation of rotating drum.
2. Description of the Related Art
There has been developed a technique in which while a rotating drum is rotated with a sheet of recording material, in particular a printing plate with a photosensitive layer on its substrate being rolled around a peripheral surface of the rotating drum (main scanning) a recording head is moved in an axial direction of the rotating drum (sub-scanning), so that an image is directly recorded onto the photosensitive layer (an emulsion surface) of the printing plate by laser beams (exposure device for printing plate). Such technique enables rapid image recording onto a printing plate.
The printing plate generally includes, in addition to the concept of a printing plate which is subjected to image recording in advance, then rolled around a plate cylinder, the concept of printing materials that image recording is performed directly on a rotating drum (including an elongated photosensitive film successively rolled around a rotating drum, a photosensitive film layer that its coating and removal are repeated, an engraving plate and the like).
According to this type of image recording device, end portions of a printing plate in a direction the printing plate is rolled around are held by a leading edge chuck and a trailing edge chuck. A position of the trailing edge chuck may be varied depending on the length of the printing plate in a direction the plate is rolled around. For this reason, a relative position of the trailing edge chuck with a rotating drum is set on the basis of information about the size of the printing plate obtained in advance.
When a rotating drum is stopped after image recording, a trailing edge chuck holding a printing plate is firstly released. Then, the rotating drum is rotated in reverse in order to successively output a printing plate rolled around the peripheral surface of the rotating drum to a discharge tray. Subsequently, a leading edge chuck is released and the printing plate is discharged outside an image recording device.
Control for stopping a rotating drum after image recording is such that a trailing edge of a printing plate rolled around the rotating drum is positioned at a trailing edge chuck releasing position in a vicinity of a discharge tray.
Thus, a sensor for detecting a rotational position of a rotating drum is provided. An amount of rotational movement (the number of pulses) since stop is instructed for the rotating drum is calculated on the basis of rotational position information from the sensor and positional information of trailing edge of printing plate. Then, the rotating drum is stopped on the basis of the result of calculation.
According to a conventional device for controlling rotation of rotating drum, however, because the rotating drum is rotating while the calculation, the position that the rotating drum is stopped is shifted by the time required for calculation. Consequently, the rotating drum cannot be stopped precisely at a trailing edge chuck releasing position.
Thus, the position that the rotating drum is stopped must be corrected during a decrease in rotational speed of the rotating drum or after the rotating drum is stopped, resulting in complicated control of the rotating drum.
The present invention is developed in light of the above-described facts, and an object of the invention is to obtain a device for controlling rotation of rotating drum that is capable of stopping precisely and rapidly a rotating drum at a predetermined position.
A first aspect of the invention provides a device for controlling rotation of rotating drum for image recording that is used for an image recording device in which a recording head is moved in an axial direction of the rotating drum so as to record an image onto the rotating drum rotating with a sheet of recording material being rolled around its peripheral surface and that controls a rotational operation of the rotating drum, comprising: rotational position detection unit for detecting a rotational position of the rotating drum at least for each rotation thereof; stop control pulse generation unit for detecting a first rotational position of the rotating drum after a stop signal for instructing stop of rotation of the rotating drum is input, and for calculating a stop control pulse on the basis of the first rotational position and generating the same; correction unit for detecting a second rotational position of the rotating drum after generation of the stop control pulse and for correcting the stop control pulse on the basis of a positional deviation with respect to the first rotational position detected when the stop control pulse started to be generated; and control unit for controlling stop of the drum on the basis of the corrected stop control pulse corrected by the correction unit.
According to the first aspect, the rotational position detection unit detects a rotational position of the rotating drum at least for each rotation thereof, and thus a rotational position of the rotating drum when detected can be known. Subsequent to a stop signal for instructing stop of rotation of the rotating drum being input, a first rotational position of the rotating drum is detected. The stop control pulse generation unit calculates a stop control pulse on the basis of the first rotational position for stopping the rotating drum at a determined stop position and generates the same. Thus, the rotating drum can be reliably stopped at the determined stop position. Further, a second rotational position that a stop processing is performed is detected. The correction unit corrects the stop control pulse on the basis of a positional deviation between the first rotational position and the second rotational position. The control unit controls stop of the rotating drum on the basis of the corrected stop control pulse. As a result, the stop position is not shifted by the time required for calculation and generation of the stop control pulse.
It is possible to precisely and rapidly stop the rotating drum rotating at high speed at a predetermined position.
A second aspect of the invention provides a device for controlling rotation of rotating drum for image recording according to the first aspect, wherein it is set to output one pulse during rotation of the rotating drum for one time, subsequent to the stop signal being input, the rotational position detection unit detects a first rotational position, the stop control pulse generation unit starts to calculate and generate a stop control pulse, a second rotational position is detected after generation of the stop control pulse and then the rotating drum is stopped by the control unit, so that a correction by the correction unit is offset.
According to the second aspect, the rotational position detection unit of the first aspect outputs one pulse during rotation of the rotating drum for one time and detects a rotational position for each of rotation thereof. Subsequent to a stop signal being input, a first rotational position is detected. The stop control pulse generation unit begins to calculate a stop control pulse and generate the same. After the stop control pulse is generated, a second rotational position is detected. Then, the control unit stops the rotating drum. Thus, a difference in rotational angle needs not to be considered. Further, a correction by the correction unit can be offset. As a result, the rotating drum rotating at high speed can be precisely and rapidly stopped at a predetermined position.
A third aspect provides a device for controlling rotation of rotating drum for image recording according to the first or the second aspect, wherein the control unit starts to decrease a rotational speed of the rotating drum after the stop signal is input and before the stop control pulse generation unit starts to calculate, stops deacceleration of the rotating drum at a time when calculation and generation of the stop control pulse become possible during rotation of the rotating drum for one time and detects a first rotational position.
According to the third aspect, the control unit of the first or the second aspect decreases a rotational speed of the rotating drum to a rotational speed that enables calculation and generation of the stop control pulse during rotation of the rotating drum for one time after the stop signal is input and before the stop control pulse generation unit begins to calculate. Then, the rotational position detection unit detects a first rotational position. The rotational speed of the rotating drum is decreased immediately after the stop signal is input. Thus, the time from when the stop signal is input to when the rotating drum is stopped becomes shorter.
A fourth aspect provides a device for controlling rotation of rotating drum for image recording according to the first aspect, wherein the rotational position detection unit outputs a plurality of pulses during rotation of the rotating drum for one time and detects a first rotational position after the stop signal is input, the stop control pulse generation unit starts to calculate and generate the stop control pulse, the rotational position detection unit detects a second rotational position after generation of the stop control pulse, and the correction unit corrects the stop control pulse by a difference of rotational angle between the first detected position and the second detected position.
According to the fourth aspect, the rotational position detection unit according to the first aspect outputs a plurality of pulses during rotation of the rotating drum for one time and a rotational position of the rotating drum can be detected for a plurality of times during its rotation for one time. Thus, a rotational position can be immediately detected regardless of a rotational position of the rotating drum. After a stop signal is input, a first rotational position is detected. The stop control pulse generation unit begins to calculate a stop control pulse and generate the same. After the stop control pulse is generated, a second rotational position is detected. The correction unit corrects the stop control pulse by a difference in rotational angle between the first detected position and the second detected position. Consequently, a stop control pulse can be immediately corrected without a stop position being shifted by the time required for calculation and generation of the stop control pulse.